Indicator 1: Water content in coal can be categorized into inherent water, external water, crystalline water, and decomposed water. Excessive water content in coal is detrimental to processing and transportation, affecting thermal stability and heat conduction during combustion and reducing coke yield and extending coking cycles during refining. The water content indicators we commonly report include: 1. Total moisture content (Mt), which refers to the sum of all inherent and external moisture in coal and is also commonly denoted as Mar. It is typically specified below 8%. 2. Air-dry basis moisture content (Mad), indicating the moisture content of coal when dried in the air. It can also be considered as inherent moisture, and in the old national standards, it was referred to as "analytical basis moisture content."

Index Two: Ash content refers to the residue left behind after coal combustion. It is not the sum of minerals in the coal, but rather the remnants of these minerals after chemical and decomposition processes. Higher ash content indicates a lower proportion of combustible components in the coal, resulting in a lower calorific value. Additionally, in the coking process of refined coal, the ash content determines the ash content of the coke. Common ash content indicators include Air-Dry Ash (Aad), Dry Ash (Ad), and also Received-Basis Ash (Aar).

Indicator 3: Volatile Matter (fully termed as Volatile Matter Yield) refers to the products resulting from the heat decomposition of organic matter and certain minerals in coal. It is not solely composed of the inherent components of coal but also includes some pyrolysis products, hence the term "volatile matter yield." The size of volatile matter is related to the degree of coal metamorphism; the higher the metamorphism degree, the lower the volatile matter yield. In combustion, it is used to determine the type of boiler; in coking, it determines the blending ratio of coal; and it is also a critical indicator for gasification and liquefaction. Commonly used types include Air Dried Base Volatile Matter (Vad), Dry Base Volatile Matter (Vd), Dry Ash-Free Base Volatile Matter (Vdaf), and Received Base Volatile Matter (Var). Among them, Vdaf is one of the important indicators for coal classification.

Benchmark Four: Fixed carbon is different from the carbon in elemental analysis, which is calculated based on moisture, ash, and volatile matter. The relevant formula is as follows: FC + A + V + M = 100, where FCad = 100 - Mad - Aad - Vad, FCd = 100 - Ad - Vd, and FCdaf = 100 - Vdaf.

Indicator 5: Total sulfur (St) is a harmful element in coal, including organic sulfur and inorganic sulfur. It can only be used as fuel if it is below 1%. Some regions require it to be below 0.6 and 0.8. The so-called environmental-friendly coal and green energy all refer to coal with low sulfur content. Common indicators include: Air-dry basis total sulfur (St.ad), dry basis total sulfur (St.d), and received basis total sulfur (St.ar).